How can a doctor tell you how long its been since you miscarried from a transvaginal ultrasound and can they be wrong if your not that far along

An : An ultrasound can detect if you are pregnant, if the fetus has a heartbeat (around 7 weeks) or if it does not have a heartbeat when it should (not a viable fetus), and if your cervix is open and a miscarriage is occuring. If you had a miscarriage and all the products of conception (fetal tissue) has passed there is no way to tell "how long it's been" since the loss occurred. Lastly, an ultrasound may not provide all the clues if read incorrectly, therefore serial blood tests to check the level of pregnancy hormone in your body will tell you exactly where you stand (pregnant or not). I am so sorry you are going through all of this. I wish you the very best.